1. FIELD OF THE INVENTION
This invention relates to self-transporting support arrangements and is particularly, though not exclusively, applicable to helicopter undercarriages. The invention extends to a helicopter having such an undercarriage.
2. DESCRIPTION OF THE PRIOR ART
A skid undercarriage is widely used in helicopters, since it permits both normal and emergency landings, while keeping weight, cost and aerodynamic drag to a minimum. Once landed, however the aircraft requires additional equipment to be moved. On firm ground, wheels can be attached, and small helicopters can then be manhandled, while larger ones can be towed. On unprepared ground, however, typically either very large wheels have to be fitted or the aircraft has to be towed on its skids by a powerful tractor. Neither of these alternatives is convenient.
Self-transporting support arrangements, which work in a manner analogous to walking, are known in connection with large apparatus such as cranes and earth-working machines. These arrangements have large ground-contacting and load-supporting "feet" which can be moved horizontally and vertically relative to each other. Motion over the ground is achieved by transferring load onto a first "foot" (or set of "feet"), raising a second "foot" and moving it horizontally before putting it down again, whereupon the load is transferred to the second "foot" so that the first "foot" can be raised and moved horizontally. In one such proposal (British patent specification No. 1,215,456) a force acting obliquely to the vertical is applied to the "feet" by a pressure cylinder through a plurality of levers which are pivotally interconnected, so that the "foot" off which weight is being transferred slides over the ground surface as soon as the horizontal component of the applied force overcomes the friction between it and the ground.